Although W and I are still negotiating some of our rules, here is pretty much what we have so far:

1. We (meaning myself and the kids) always come first. Although this is a very vague statement, so far what we've meant it is we will always have more face time with her than her guy does, we'll always be considered first in case of scheduling conflicts, and the like.
2. No mixing of finances. This means no paying bills, buying expensive gifts, etc. for her guy.
3. No stays over 24 hours (although we're still negotiating this part).
4. Kids are not exposed to our lifestyle. They are not to know he is anything other than a good friend. No romantic gestures towards him while they're around, no having him over to our home while they're there and I'm not, and no referring to him as a boyfriend, lover, father-figure, etc.
5. We only expose our lifestyle to those people that we've all three agreed upon.
6. Any three of us are welcome to persue other relationships without getting consent of the others.